This invention relates generally to electrostatography, and more particularly, concerns a low cost process multicolor image reproduction machine.
Generally, processes for electrostatographic copying and printing are initiated by selectively charging and/or discharging a charge receptive imaging member in accordance with an original input document or an imaging signal, generating an electrostatic latent image on the imaging member. This latent image is subsequently developed into a visible image by a process in which charged developing material is deposited onto the surface of the latent image bearing member, wherein charged solids in the developing material adhere to image areas of the latent image. The developing material typically comprises carrier granules having charged marking or toner solids adhering triboelectrically thereto, wherein the toner solids are electrostatically attracted from the carrier granules to the latent image areas to create a powder toner image on the imaging member.
Alternatively, the developing material may comprise a liquid developing material comprising a carrier liquid having pigmented marking solids (or so-called toner solids) and charge director materials dispersed and/or dissolved therein (so-called carrier liquid), wherein the liquid developing material is applied to the latent image bearing imaging member with the marking solids being attracted to the image areas of the latent image to form a developed liquid toner image. Regardless of the type of developing material employed, the charged toner or marking solids of the developing material are electrostatically attracted to the latent image to form a visible developed image corresponding to the latent image on the imaging member.
The developed image is subsequently transferred, either directly or indirectly, from the imaging member to a copy substrate, such as paper or the like, to produce a xe2x80x9chard copyxe2x80x9d output document. In a final step, the imaging member is cleaned to remove any charge and/or residual developing material therefrom in preparation for a subsequent image forming cycle.
The above-described electrostatographic printing process is well known and has been implemented in various forms in the marketplace to facilitate, for example, so-called light lens copying of an original document, as well as for printing of electronically generated or digitally stored images where the electrostatic latent image is formed via a modulated laser beam. Analogous processes also exist in other electrostatic printing applications such as, for example, ionographic printing and reproduction where charge is deposited in image-wise configuration on a dielectric charge retentive surface. It will be understood that the instant invention applies to all various types of electrostatic printing systems and is not intended to be limited by the manner in which the image is formed on the imaging member or the nature of the latent image bearing member itself.
As described hereinabove, the typical electrostatographic printing process includes a conventional development step whereby developing material including charged marking or toner solids is physically transported into contact with the imaging member so as to selectively adhere to the latent image areas thereon in an image-wise configuration. Development of the latent image is usually accomplished by electrical attraction of charged toner or marking solids to the image areas of the latent image. The development process is most effectively accomplished when the solids carry electrical charges opposite in polarity to the latent image charges, with the amount of toner or marking solids attracted to the latent image being proportional to the electrical field associated with the image areas. Some electrostatic imaging systems operate in a manner wherein the latent image includes charged image areas for attracting developer material (so-called charged area development (CAD), or xe2x80x9cwrite whitexe2x80x9d systems), while other printing processes operate in a manner such that discharged areas attract developing material (so-called discharged area development (DAD), or xe2x80x9cwrite blackxe2x80x9d systems).
The process described above is suitable for producing monochrome or single color toner images. Multicolor toner images can also be produced using anyone of several well known methods representing variations from the monochrome or single color process.
In general, to produce multicolor images, different color components of a composite color image are formed and then put together in registration to achieve the composite color image. One multicolor image production method, for example, involves a process utilizing a plurality of different color toner development units, a single photoreceptor, and a multiple image frames single pass approach in which the monochrome or single color process is repeated for three or four cycles. In each cycle a component latent image of a composite multicolor final color is formed, and a toner of a different color is used to develop the component latent image.
Each developed component image as such is then transferred to the copy sheet. The process is repeated, for example, for cyan, magenta, yellow and black toner particles, with each color toner component image being sequentially transferred to the copy sheet in superimposed registration with the toner image previously transferred thereto. In this way, several toner component images, as are in the composite image, are transferred sequentially to the copy sheet, and can then be heated and permanently fused to the sheet.
A second method for producing color copies involves what is referred to as the tandem method which utilizes a plurality of independent imaging units for forming and developing latent component images, and a moving image receiving member such as an intermediate transfer roller or belt. In this method, the toned or developed component images from the imaging units are transferred in superimposed registration with one another to the intermediate roller or belt, thereby forming the multicolor composite image on the belt or roller. The composite image then can be transferred in one step to a sheet of copy paper for subsequent fusing.
A third method for producing color copies involves a single frame, single pass Recharge, Expose, and Develop (REaD) process. The REaD process uses a single photoreceptor, a single image frame thereon, and four imaging units each including imagewise exposure means and a development station containing a different color toner of cyan, magenta, yellow or black.
A composite subtractive multicolor image can thus be produced in a single pass, and on the single frame by charging, exposing and developing, then recharging, exposing and developing again utilizing this Recharge, Expose, and Develop (REaD) process architecture. In this process, digital version of the original or document is created pixel by pixel at a computer workstation or by a scanner. When created by scanning, light reflected from the original or document is first converted into an electrical signal by a raster input scanner (RIS), subjected to image processing, then reconverted into a light, pixel by pixel, by a raster output scanner (ROS).
In either case, the ROS exposes the charged photoconductive surface to record a latent image thereon corresponding to the subtractive color of one of the colors of the appropriately colored toner particles at a first development station. The photoconductive surface with the developed image thereon is recharged and re-exposed to record a latent image thereon corresponding to the subtractive primary of another color of the original. This latent image is developed with appropriately colored toner. This process (REaD) is repeated until all the different color toner layers are deposited in superimposed registration with one another on the photoconductive surface. The multi-layered toner image is transferred from the photoconductive surface to a sheet of copy paper. Thereafter, the toner image is fused to the sheet of copy paper to form a color copy of the original. The REaD process can also be performed as a multiple pass process.
Machines for carrying out each of the conventional multicolor processes as described above, typically include a large number of expensive components, and a long cycle, and hence a long process, which together result in an undesirably high cost per copy of each multicolor image they produce.
There is therefore a need for a multicolor image reproduction machine that has very few components and a relatively very short cycle, thus resulting in a cheaper (relative to cost of conventional) cost per copy produced.
In accordance with the present invention, there is provided a low cost process multicolor image reproduction machine includes a rotatable endless toner image receiving and transfer member for cyclically building up a multicolor image from a plural number of received color separation toner images; a sheet handling system including a back up roller defining a toner image transfer nip against the rotatable endless toner image receiving and transfer member; a rotatable photoreceptor member forming a contact electrostatic printing (CEP) nip with the rotatable endless toner image receiving and transfer member for separating toner image areas from toner background areas of a color separation toner image formed on the photoreceptor member; imaging devices for cyclically forming a plural number of color separation toner images on the photoreceptor member, and a controller for controlling formation of, and build up into a multicolor toner image, of the plural number of color separation images, as well as, transfer of the multicolor toner image onto a copy sheet.